1. Field of the Invention
The present invention relates to a sheet folding apparatus that folds a large-sized sheet to file it in a regular-size folder neatly and further punches holes in the sheet for filing, and to an image forming apparatus using the sheet folding apparatus. The present invention relates to, although not intended to limit the invention, a sheet folding apparatus that folds an A2, A1, or A0 size sheet into A4 size and punches holes in the sheet with a puncher for filing the sheet in an A4-size folder. The sheet folding apparatus can be used in a finisher, or a folding apparatus, provided with an edge folding and punching function. The sheet folding apparatus can also be connected and used with a copier, a facsimile, a printer or a plotter.
2. Description of the Related Art
Punchers for punching holes in a sheet at predetermined positions, edge (corner) folding devices that fold an edge of a sheet, and combinations thereof, each of which are to be provided in a sheet folding apparatus, have been proposed in various types. The sheet folding apparatus is connected to an image forming apparatus such as a printer, a copier, or a facsimile, and folds a sheet in a predetermined mode.
Each of Japanese Patent Application Publications Nos. H8-29884, H7-35222, and H5-525548 proposes a sheet folding apparatus capable of folding a sheet of A2 size or smaller into a regular size, punching filing holes in the sheet, and further printing a stamp on the sheet. More particularly, Japanese Patent Application Publication No. H8-29884 discloses a mechanism that folds a sheet into two, Japanese Patent Application Publication No. H7-35222 discloses an edge folding mechanism, and Japanese Patent Application Publication No. H5-52548 discloses a positioning mechanism that positions a sheet to be punched relative to a punching unit, respectively, in detail. Japanese Patent Publication No. 3173121 proposes an edge folding device having a pair of edge folding mechanisms each lifting up a leading end corner of a sheet to be folded to fold back the corner. Japanese Patent Application Laid-open No. 2002-128385 proposes a sheet processor attached to an image forming apparatus and including a punching device that can punches two, three, or more holes in a sheet fed from the image forming apparatus.
However, according to the conventional technique, only a punching device or an edge folding device is mounted on a post-processing apparatus as in the case of, e.g., the sheet post-processing apparatus described in Japanese Patent Application Laid-open No. 2002-128385 that includes the punching device capable of punching two, three, or more holes in a sheet fed from the image forming apparatus, or the edge folding device described in Japanese Patent No. 3173121 that is provided in the sheet folding apparatus for folding a large-sized sheet such as a drawing draft into a small size and folds back an edge (leading end corner) of the sheet. Accordingly, it is necessary to punch holes in the sheet output from the edge folding unit using a puncher or manually to file the sheet in a file (regular-size folder), which places a large burden on an operator.
Because it is necessary for each of the sheet folding apparatuses described in Japanese Patent Application Publications Nos. H8-29884, H7-35222, and H5-525548 to change an orientation of a folded sheet relative to a puncher according to a size of the sheet, each sheet folding apparatus includes a sheet rotating mechanism that rotates (reorients) a sheet by 90 degrees about an axis perpendicular to a sheet plane. For example, an A3 sheet delivered in horizontal orientation or an A4 sheet delivered in vertical orientation is rotated by 90 degrees and thereafter fed to a punching stage. A maximum available sheet for these sheet folding apparatuses is an A2 sheet in vertical orientation (hereinafter, “A2 vertical”). Accordingly, among A2, A3, and other A-sized sheets, sheets that need to be rotated by 90 degrees are only an A3 sheet in horizontal orientation (hereinafter, “A3 horizontal”) and an A4 sheet in vertical orientation (hereinafter, “A4 vertical”), which are relatively small-sized sheets. To allow these sheets to be rotated by 90 degrees, a requirement for the sheet folding apparatus is only being capable of accommodating a circle having a diagonal line of an A3 sheet as its diameter therein. Hence, an increase of the sheet folding apparatus in size can be suppressed. However, in a sheet folding apparatus of which maximum processable sheet is an A0 sheet in vertical orientation (hereinafter, “A0 vertical”), the sheet folding apparatus is required to be capable of accommodating a circle having a diagonal line of the A1 sheet as its diameter to allow an A1 sheet to be rotated in horizontal orientation. To meet this requirement, the sheet folding apparatus must be significantly increased in size.